An attempted controlled explosion damaged the vessel during clean-up operations, city disaster management spokesman Wilfred Solomons-Johannes said yesterday.
One of the tanks ruptured in the explosion "releasing oil that was onboard the wreck," Solomons-Johannes told the national Sapa news agency.
Conservation officials were monitoring the spill, which hadn't put the environment in immediate danger, he added.
This was the second spill from the wreck in a year.
In September, it leaked oil onto the city's beaches after breaking up into three pieces.